HOMOPOLYMER DISTRIBUTIONS IN LAMELLAR COPOLYMER HOMOPOLYMER BLENDS

A quantitative mean-field treatment, based on the representation of polymer chain statistics by probability distribution functions, is applied to lamellar blends of an AB diblock copolymer with an A homopolymer. We work in the strong segregation limit, where the interface between A and B microdomains is narrow and the A homopolymer segregates exclusively to the A domain. Copolymer blocks are modeled as end-adsorbed "brushes' which are anchored to opposing sides of a microdomain. Numerical solution of the mean-field equations can be used to determine homopolymer and copolymer profiles for all blend compositions. For pure diblock copolymers we obtain a simple analytic expression for the width of the overlap region between opposing copolymer brushes. Similar analytic expressions are obtained for the homopolymer distribution in blends for which the homopolymer molecular weight is larger than the molecular weight of the corresponding copolymer block. Numerical solutions to the mean-field equations are given for a set of experimentally studied copolymer/homopolymer blends. Fundamental aspects of lamellar copolymer/homopolymer blends, including those with low molecular weight homopolymers, are discussed in the context of this well-characterized model system.